Electron discharge device



June 27, 1950 H. R. HEGBAR ELECTRON DISCHARGE DEVICE 5 Sheets-Sheet 1 Filed Oct. 25, 1945 June 27, 1950 1-1. R. HEGBAR ELECTRON DISCHARGE DEVICE INVENTOR MW ATTORNEY 5 Sheets-Sheet 2 flowrd/Zflgzbar Filed Oct. 25, 1945 June 27, 1950 H. R. HEGBAR 2,512,858

ELECTRON DISCHARGE DEVICE 6/ %w/zzw )2 Q4 60 V ATTORNEY June 27, 1950 H. R. HEGBAR 2,512,353

ELECTRON DISCHARGE DEVICE Filed Oct. 25, 1945 5 Sheets-Sheet 5 INVENTOR ATTORNEY Patented June 27, 1950 ELECTRON DIS CHARGE DEVICE Howard B. Hegbar, Princeton, .N. J., assignor .to 'Radio Corporation of America, a corporation of Delaware Application October 25, 1945, Serial No. 624.360

37 Claims. 1

My invention relates toelectron discharge devices, more particularly to amplifier tubes useful at very high frequencies and delivering large amounts of power.

The provision of a tube which willoperate at very high frequencies and-deliver large amounts of continuous power with reasonable bandwidth and power gains presents serious problems incapable of solution with conventional tube designs.

The dissipation of heat, which is'one of the most serious problems and which must be accomplished to protect scalsand electrodes and to prevent undesired electron emission, requires structures which "with conventional design adverseiy aii'ect the electrical characteristics of the dev'ce in the way of increased inductances and capacitances and increased electron transit times. This limits operation at high frequencies, particularly-when the desired band width is that required for television. Heat causes expansion and contraction of the tube elements, thus aiiecting P cings and alignments and operating stability. Zine need to dissipate heat from all electrodes and elements introduces further cooling problems since for high frequency operation small structures and close spacings are a prerequisite.

High frequency operation on the other hand requires small electrodes and leads and close spacing to reduce interelectrode and lead capacitance, and inductance and to limit the transit time of the electrons between the electrodes to-such value that the transit time does not become an appreciable percentage of the period of oscillation. That is, the transit angle must be small.

i-Towever, close spacing increases interelectrode capacitances and consequently the electrode area must be decreased and thus for high power output cooling becomes diflicult with such compact structures.

.At high frequencies stable and efhcient operationcan be had only by properly isolating the inand output circuits and electrodes.

To obtain high .power outputs at reasonable anode voltages and to encourage decreased transit angles, high current densities are required. This requires proper field and electrode configurations.

Further, when the transit times for all simultaneously emitted electrons cannot be made small, substantially equal transit times for electrons simultaneously emitted from various parts of the cathode surface are desired so that the upper frequency limit of operation at which normal electronic efficiencies may be obtained is not decreased. In addition the current must be formed into beams to reduce electronabsorption by the control and screen-.grids, which absorptionby the grids would increase grid'heating and undesired grid emission and decrease the amount of useable current to the anodes. Conventional beam-forming electrodes; however,complicate tube structure, introduceundesired capacitance and-inductance and aggravate the cooling problems.

In push-pulloperationat high frequencies neutralization to. prevent spurious oscillation is a problem since short leads are required to minimize phase shift. When two tubes of the tetrode type are operated side by side in push-pull-operation the screen grid structures, leads and external screen connections utilized become an oscillating circuit and impose undesired resonant conditions on the tubes. Furthersmall differencesin tube structures result in unbalanced push-pull-amplifier circuits.

The conventional methods of cooling an anode when'the tube isdesigned for high power output -athigh 'frequenciesiare not always efiective because of the inability to .dissipate largeamounts of generated heat rapidly from small closely spaced electrodes.

The manufacture-of a tube of the type described is also complicated by the close spacings and accurate alignments required.

It is, therefore, a principal-objector my-invention to provide-an improved'electron discharge device particularly useful as an amplifier and delivering large amounts of power-at ultra high frequencies.

Another object of my invention is toprovide such a device, particularly suitable as a push-pull amplifier, having substantially complete electrical'stability and freedom froln oscillation.

A- further objectof'my invention-is to-provide such adevicehaving a small average grid current,

3 sembly which minimizes electron absorption by the control and screen grids.

Another object of my invention is to provide an electron discharge device having small electrode structures, short leads and close spacings yet capable of large continuous power outputs at high frequencies and in which eificient cooling is obtained and in which interelectrode and lead capacitances and inductances are maintained at very low values.

A still further object of my invention is to provide novel and eflicient cooling of all seals and electrodes thereby increasing the power output capacities of the small electrodes and leads essential for high frequency operation.

More specifically it is an object of my invention to provide an improved method and means for cooling the output electrode or anode.

Another object of my invention is to provide a device having precision parts which can be accurately and easily assembled and aligned and in which alignment and spacing are rigidly maintained during operation, thus minimizing change of electrical characteristics.

A still, further object of my invention is to provide such a device suitable for push-pull operation and having an improved internal neutralizing means.

A further object. of my invention is to provide an electron discharge device for push-pull operation in which balanced push-pull operation is insured.

Another more specific object of my invention is to provide an improved means for shielding the input and output circuits and electrodes from each other.

A further object of my invention is to provide means for fluid cooling of the cathode support, control and screen grids.

A still further object of my invention is to provide novel improved constructions of the oathode, control grid, screen grid and anode electrodes resulting in improved characteristics and efiiciencies.

The novel features which I believe to be char- 7 acteristic of myinvention are set forth with particularity in the appended'claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a schematic diagram of an electron discharge device employing the principles of my invention, Figures 2 to 6, inclusive, are schematic cross sectional diagrams of focusing arrangements which may be employed with my invention, Figure 7 is a sectional perspective showing the relative shapes and positions of the electrodes employed in my invention, Figure 8 is a side elevation, partially in section, of an electron discharge device employing my invention, Figure 9 is a section taken along the line 99 of Figure 8, Figure 10 is a longitudinal transverse section taken along the line Ill-l B of Figure 8, Figure 11 is a partial transverse section taken along the line Hl| of Figure 10, Figure 12 is an end elevation of Figure 8 with parts in section showing details of construction, and Figure 13 is an exploded perspective of the electrodes comprising the mount construction of the electron discharge device shown in Figures 8 to 12, inclusive.

Briefly, an electron discharge device made in accordance with my invention includes an evacuated envelope containing a mount assembly comprising two electron emitting cathodes, two first or control grids, two second or screen grids and 4 A two anodes with neutralizing elements all combined and disposed to form an internally neutralized duplex tetrode. The neutralizing elements may be attached to either the grid or anode of one tetrode section and perform the function of neutralization by means of direct capacitance between the neutralizing element and the grid or anode of the other tetrode section when the tube is operated as a push-pull amplifier.

The schematic arrangement of such a tube is shown in Figure l in which the double cathode it has mounted on either side control grids ll- 52, screen grids l3l4 and anodes lB--ll, the neutralizing capacitances being indicated at it and I8 and the by-pass capacitance between the screen electrode and cathode being shown at all the electrodes being mounted within a common envelope 21. The cathode is grounded to the envelope and the screen grids are combined to form a unitary screen grid structure. Shielding- 22 is connected to the screen grid structure and shields the control grid circuits from the anode circuits.

In order to provide controlled beams having high current densities and to permit the close spacing of the control and screen grids, which is required for efiicient high frequency-high power operation, the electric field and electrode configurations become important.

In the practice of my invention the electric field configuration at and near the cathode is of such form that the emitted electrons are focused to form a beam passing between the grid elements, the electric field configuration being obtained by means of fluted or planar focusing elements operating at a zero or negative potential with respect to the planar or fluted cathode elements.

A number of such arrangements are disclosed in Figures 2 to 6, inclusive, wherein C is the oathode and F the focusing elements. The dashed lines indicate the electron paths. The electric field near the electron emitting surface is such that the electrons leaving this surface are subjected to a force which has a component directed toward an axis through the center of the emitting surface and perpendicular to it, this force component being greatest in the region of the edges of the electron emitting strips. Such electric fields are produced by electrode configurations shown where the focusing electrodes F are at cathode potential or negative with respect to it. Any of these arrangements may be utilized with my invention.

However, I prefer to utilize the arrangement shown in perspective in Figure 7. In this arrangement the focusing electrode may be formed from a planar solid block 2? having a plurality of parallel grooves or slots 26 within which are received the flat strip or ribbon-like cathode filaments 25. Mounted above and in registry with the portions of the focusing electrode intermediate the slots 26 are the control grid rods 28 also preferably of rectangular or beveled rectangular cross sectional shape and registering with these rods 28 are the screen grid elements 29. The purpose of the concave surface 3| of the portions of the focusing electrode is to reduce the capacity between the control grid elements 28 and the focusing electrode elements of electrode 21. An anode 3|] receives the electrons from filament cathode 25.

With the focusing elements formed and arranged as shown an adequate focusing electric fielduis. producedat ornear. the cathode surface:

Without theelectrodes .themselvesprojecting ape preciably. in the direction ofithe anode, thus. per,- mitting; control .gridsebeing. placed in close proximity. to .thelplane of the. cathode which is, desirelements,- provide effective control of the electron beam and act like thin element's with small electron absorption from the. beam but. nevertheless have a substantialcross section, forconducting;

heat to the. mounting, pipe. onwhich these elements. are supported. and for maintaining. me-

chanicalrigidity, andstability. These electrode.

elements. provide asmaller effective electrode spacing for. comparable clearances when compared to moreconventional. or circular section elements. Testswith control grids utilizing such crosssectionalt areas show. that increased beam current. densities may. becontrolled with. decreasedgrid currents.

The. planar or concave electron emitting surfacesof. the strip cathode elements function to provide substantially equal transit times for electrons simultaneously. emitted .from various parts ofthe cathode surface. substantially. different transit times from the average, as may. be encounteredin conventional squirrel-cage structures,v will necessarily have longer transit times, this. effect tends-to increase the upper frequency of operation at which normal electronic efliciencies may be obtained. These strip cathodes also deliversubstantial electron emission-current.densities-with a minimum of magnetic modulationof the electron trajectories and are superior to cathodeelements of cir.- cularcross section in this respect.

Because of the. increased electron currentdensitieswhich may be utilized (in practice 3.5; amperes\per square centimeter of cathode surface have beenobtained and successfully utilized) and the decreased effective, electrode spacings, the transit angle of grid. controlled amplifier tubes made according to my invention .issubstantially decreased. It maybeshown that, for parallel plane electrodes,

where d-isthe transit angle from cathode to grid plane, J isthe electron beam current density and Sis the effective spacing between cathode and grid, thisbeing the region of interest for transit angle consideration for the operation of this invention. Since. these field and electrode configurations permit increased electron current densities and decreased transit-angles, new high frequencywideband power amplifier tubes are made possible, such tubes operating at 300 megacycles with 5 kilowatts output and a total bandwidth inexcess-of megacycles.

Amelectron discharge device made according to myv invention andembodying the principles describedgabove is shownin Figures 8 to 13, inclusive,.

Essentially the cathode and focusing electrode assembly comprises liquid cooled metallic focusing a-ndmountingblocks with a multi-filament u-shaped cathode encompassing and clamped to th se blocks, The electron emittingsurfaces of theycathode maybe of pure metal, such. as tanta- Since. electrons having lum, or may be oxide: coated 1 on. a. metal. strip.. The focusing elements are an integral part-.otthe. cathode mounting blocks. Briefly: the. cathode comprises an elongated U-shaped member iIJ-Cllld'.

- ing a pluralitysof;electronemitting strips parallel to each other and received within parallelfocus-v ing grooves or slots on-the cathode block.

Referring specifically to Figures 10, 11 andlS,

the cathode andfocusing electrode assembly com.-

: prisesthe focusingelectrode blocks, and.36.-:in.-

sulated from each other by means of the mica separator.- or spacer 38. and provided with aplus. rality of-Jparallel rectangular slots 31 into which. the emitting elements of the .cathode are posi-= vtioned; These blocks are clamped together; in.

the mountasseinbly. by. means of screws 35. and: 35' insulatedfrom one of the focusingblocks- These blocks are in turn supported by and clamped between the liquid-cooled header mounting blocks 39 and 40 insulatedfrom-each other by means of' the mica spacer 4|. One block is provided-with the extension 4| for clamping the assembly-to the header-in amanner-to'bedescribed. The focusing blocks orelements are secured to the mounting blocksbymeans-of the crews 42, 42.

The cathode comprises a plurality of elongated U-sh-aped elements 41' secured atthe ends of thelegs by meansof the elements 48, 48", the elements 4'! lying in parallel planes. These emitting elements are received within the slots 3 of the focusing blocks and nested within the slotsbelowa plane passing through the outer'surfaces of the portions of the focusing block betweentheslots, the relationship being as clearly disclosed in Figure '7; As shown in Figure. 11 the cathodeand; the cathode shields 5i! and .51 are secured to the focusing block by means-ofscrewsfii and .52? so that the clamped ends ofthe U-shapedcathode filamentsare shielded against emission. A catha ode shield .52.is sccuredto the endofthe cathode. focusing blocks to cover: and prevent emission from,the closed'end of the U.-shaped cathode. filamentsandanother shield53 is'positioned at: the bottom of the focusing elements to. prevent the: emission of stray. electrons which would miss. the anodes andbombard thelglass envelope. It is evident that there .is thusprovideda unitary water-cooledcathode and focusing electrode assembly forprovidinga plurality of parallel beams directed from opposite. surfaces of the planar. structures.

The cathode and focusing structures described provideelectronic, circuit and mechanical advantages that are of particular significance when these structures are incorporated in amplifier tubes. These structures provide and permit liquid cooling of the mounting, supporting andlead-in structure in a manner to be described and thereby, reduce thermal expansion sufficiently to maintain the electrode alignment in normal operation substantially that introduced during assembly. The accurate alignment that can be obtained during assembly and maintained during normal operation along with the mechanical symmetry of the described structure makes possible a rid-tocathode and grid-to-screen grid capacitance balance between two tetrode sections of the duplex tetrode amplifier tube together with small spacings and very low control grid and screen grid current pickup from the high density electron beams.

The cathode and focusing structure described provides a low impedance electrical connection between the individual. cathode and focusin eles ments of each tube section and between the two cathode and focusing sections of the duplex tube. Such low impedance is advantageous in ultra high frequency push-pull amplifiers.

The method of cathode mounting and the mounting structures make it possible to provide a screen grid-to-cathode bypass arrangement to be described, which is of low electrical impedance and has connections of extremely low inductance. In this arrangement an efficient and compact capacitor can be utilized because it canbe mounted within the vacuum enclosure. Further, the structure with the focusing elements formed in the cathode block provides a low-resistance cooled metallic conductor as the focusing element which also acts to conduct most of the input grid charging currents induced during operation of the device.

The control grid structure is placed next adjacent the cathode and cathode focusing electrode assembly. The grid assembly is composed of a metallic tube or pipe sealed through and supported by a glass seal of the envelope and into which wires or slats are fixed with good thermal and electric contact, the slats being mounted transversely to the supporting pipe axis and functioning as the controlling elements. The element length is chosen relative to the element cross section so as to permit all of the power dissipated in the elements to be conducted to a coolant circulated in the supporting pipes. The mechanical mounting and positioning of the elements is obtained by means of holes or slots machined in the supporting pipe or in a metallic block or strip, which can be secured thereto. The neutralizer structure referred to above consists of metallic lugs fixed to the grid supporting tube and rojecting through the screen grid enclosure.

Specifically, each control electrode comprises the tubular pipes 56 and 56' having slots for receiving the transverse parallel spaced control grid elements 55, 55' having elongated rectangular shaped transverse sections. Inner tubes 51, 57' serve to conduct a coolant into or out of the pipe 56, 56' serving as the grid element supports. To provide neutralizing elements, the pipes 56 are provided with L-shaped lugs 58 and 58, carrying the elements 59 and 59' which serve to provide capacitance coupling to the anodes to be described. Each of these grids is electrically insulated and separately supported by a seal through the tube header in a manner to be described.

The grid structure described above provides a sturdy mechanical support and accurate alignment and spacing of the elements that is maintained during normal operation of the device in which the grid is mounted. This is obtained by the effective cooling of the supporting tubes and the attached glass seal to be described, which eliminates misalignment of the electrodes by thermal expansion due to energy absorbed by the control grid elements or power dissipated in the supporting and lead-in pipe. This effective cooling of the supporting pipe provides a means for cooling the control grid elements and thus prevents excessive electron emission from the elements.

The neutralizer arrangement and structure permits a minimum length and consequently minimizes the phase shift due to neutralizer lead length. This arrangement is especially adaptable to duplex tetrode amplifier tubes made according to my invention.

Surrounding the cathode assembly and control grids is a screen grid which is fluid cooled and of unitary construction. This unitary structure is in the form of a box-like frame having open sides and having grid elements spaced and aligned by means of slots machined in the metallic frame, the elements being silver soldered or otherwise fixed to theframe with good thermal and electric contact.

Still referring to Figures 10, 11 and 13, this unitary screen grid assembly comprises a pair of more or less U-shaped members 60 and BI. The U-shaped members 60 and BI are secured to the end block members 54 and 55 to form a box-like structure open at the sides, the screen grid elements being positioned within these open spaces. Members BI! and SI are provided on the outside and along the inner edges of the legs with bevelled surfaces 62, 63, 64 and 65, these U-shaped members 60 and GI being provided with inwardly extending portions 66, 61, 68 and 69 provided with slots in which the screen grid rod-like elements ll and 72 and H and 72' are positioned and fixed to the U-shaped members. The positioning of the elements on the inside face of the U-shaped members Bil and GI provide a pocket in the outside sides of the screen grid to receive the anodes to be described. As shown in Figures 10 and 11, these screen grids are secured to the members 74 and 75 by means of the screw members such as 14' and 15'. These members M and 75 are in turn clamped to the cathode supporting blocks but insulated therefrom by means of the insulating spacers 16 and 11 preferably of mica, the bolts 19 being insulated from the elements which are clamped by means of the insulating spacers 79. The mica spacers position the attaching blocks 74 and 15 in capacity relationship with the cathode cooling blocks so that radio frequency current from the screen grid may be bypassed to ground through one of the supporting blocks. The U-shaped members to and 61 are provided with apertures Eli and 6! through which the lugs 58 and 58 supporting the neutralizing elements 59 and 59 extend. Itwill thus be observed that the cathode and focusing electrode and the unitary screen grid are supported as a rigid compact structure from the header member.

Because of the arrangement described, the screen grid and mounting structures provide circuit, thermal and mechanical advantages. Several circuit advantages accrue from the compactness and low impedance connections between elements and electrodes. Such low impedance paths are provided between the screen grid elements, between the two screen grid se tions of the duplex tetrode and between the screen grid structure and the cathode. Of equal importance in ultra high frequency amplifiers is the very short length of neutralizer elements which is permitted with the type of screen grid structure described. All of these features combine to provide electrical stability in an ultra high frequency duplex tetrode amplifier.

The screen grid structures provide precision alignment of the elements which in unaffected by the processing temperatures and normal operating conditions when the proper metals are utilized. The method of mounting elements permits effective cooling by circulating a coolant in a manner to be described.

The anode consists of a metallic multi-channel block in which a coolant can be circulated, the coolant being introduced by means of tubular anode supporting leads. The tubular anode sup-v 9. porting leads are arranged and constructed so as to function as elements of the anode resonant circuit formed by connecting the leads together with a shorting bar.

Referring to. the drawings, Figures 10, 11 and 13, two part anodes 88, 8| and .86 and 8| each comprises the same elements such as the electron receiving. portion tlihaving a plurality of longitudinall extending fins 82 and 83, the fins being displaced longitudinally to provide a space at alternate ends. between the fins and the enclosing ends of theportion. 8.I, which receives the member .80. Apertures 84 are provided through whieha coolant may be introduced to circulate through the .multi-channel path of the anode. The two. parts of the anode may be silver soldered together.. To the rear of the part 8| is extended a portion 85 which isprovided with collar 8% received within outer tubular member 31 enclosing a pair of telescoped inner tubular members 88, dill. This portion 85 is provided with the passageways 83 and 89? as indicated in Figure 11 for the passage of a cooling medium through the anode. The cooling medium is introduced through the outer tubular member and directed out'of the anode through the inner tubular member 88, the cross sectional area of which is smaller than the cross sectional area of the spacev between the two tubes whereby static pressure of the coolant .within the anode may be built up for the purpose of increasing the powerdissipation of theanode with a given coolant flow.

Since the lead duct of. greatest hydraulic impedance is utilized as thecoolant exhaust duct, a greater static pressure is obtained in the anode channels with a fixed supply pressure. This greater static. pressure permits a higher temperature ofth'e metallic anode block and consequently a greater powerdissipation before excessive steam bubbles are formed.

The anode, comprising the portions 80 and BI, is positioned onthe: opposite side of the mount assembly fromanode 8B, 81. and has like parts indicated by like. primed numbers. Each of these anodes is separately supported and insulated from the other by the tubular members in. a manner to be described.

The anodestructures and the arrangement of the cooling. ducts" described provide an average electron bombardment power input per unit area of bombarded surfacein excess or" 800 watts per square centimeter with a. reasonable water flow and pressures not in excess of 70 pounds per square inch. .Slip joints are used in the center cooling pipe as; shown, which prevents deformation ofthe lead tube and seal during baking and processing.

The envelope and header assembly to be described and made according to my invention provides, a method and means of mounting vacuum. tube parts to a plate or other rigid member which is part of the vacuum enclosure and adjustable withrespeot to the remainder of the vacuum envelope. and electrodes aiiixed thereto.

Referring, tdFigure 10 the headermember or plate 90 is provided with certain apertures and leads extending therethrough and tobe described. The header members!) is provided with a supporting block i l .amxed thereto to which the cathode. and screen grid assembly are bolted by means of bolts 52. Thus the screen and cathode are supported. directly by the. header plate 953. The envelope-comprises collar-shaped member 93 provided. with flange 941 and a cup-shaped a- It enclosure 95 which completes the envelope. The header is securedto the flange 94 by means of the bolts 98, and gasket member 99 is utilized for securing a vacuum-tight seal. or gasket I00 is introduced to prevent warping of the header platewhen bolted. The adjustment of the header plate with respect to the dome assembly is provided'by means of the holes in the header plate, which are machined oversize and permit lateral movement of the-bolt and dome assembly with respect to the header plate. An exhaust tube I28 is provided for exhausting the envelope.

The adjustable. header method of tube construction and assembly according to my invention provides a practical method for the construction of evacuated devices requiring closely spaced elements. A duplex tetrode is such a device. The

cathode, control grids and screen gridsmay. be.

conveniently assembled, aligned and spaced-with the header plate removed from the envelope.- The described methods of joining the header. plate to.

the envelope provide adjustment which permits.

an accurate balance in spacing and capacitance between the anodes and screen grids of. the. two tetrode sections.

When the vacuum vessel is assembled as described the resulting convenient disassembly.

makes practical the-repair of a damaged device and increases its salvage value.

The combined. support and. cooling. leads for the electrodes and seals form. an essential. part of a device made according to my invention. Referring to Figures8, 9, 10, 11 and. 12, the-cathode-blocks 39and 40 are provided withpassagesin which the cooling. pipes IOI and. I02 may be inserted. The ends of tube IOI extendthrough and-are sealed in theheader plate 90.as shown inFigu-re 12.v The ends of the cooling pipe Ill-2. extend through an aperture in. the headerv plate and through the plug. I03 to which the pipe isv hermetically sealed and through which the ends pass. The plug I03 is sealed in the lower end of tubular member I04 surroundedby tubular member [05 sealed in turn to the header. A seal I06, preferably of glass, is made betweenthe two tubular members. These pipes IOI and I02 serve not only to convey thecoolant to and from the cathode blocks but also as the leads for supplying the cathode current. Itis obvious that the blocks could be drilled to provide a passageway therethrough and tubular leads soldered tothe block to communicate with these passageways.

The screen grid. assembly is likewise liquid cooled and as shown in Figure 8 each U.-shaped member is providedwitha U-shaped passageway, such as IIO, extending. therethrough. As best shown in Figures 8, 9 and 12, a. pair of tubular conductors H2 and H3 communicate with the passageways in the U-shaped screen-grid elements and are joined together by the coupling tubular member II4. These tubular members extend through and are sealed in. the plug II5 supported by tubular member H6 coaxiaLwith the tubular member II'I sealed to the header block 99. An insulating and hermetic seal II8 is made between the tubular members. These cooling pipes and leads also provide. the leads for applying the positive voltage to the screen grid electrode.

As shown in Figures 8, 9 and 12, the control grids are each separately supported by the hollow conductors 5! and 51' passing through the collar I20 to which is sealed dome shaped insulating member I2I through which and to which The spacing ring the tubular members 51 and 57 are sealed with a vacuumtight seal. The inner and outer pipes 56,5! and 56' and communicate with the tubular extensions I22, I23, I22 and I23 into which and out of which a coolant may be circulated to maintain the grid cool.

The anode is supported from the insulating dome shaped portion of the envelope and sealed to this portion as shown in Figures 8, and 12, a seal being made at I25 and I26 forsupporting the anodes in proper spaced relationship with respect to the other electrodes within the tube.

A skirt-shaped shield I21 connected to the screen electrode extends between the screen electrode and the header and completely shields the control grids and control grid leads from the anodes and the anode leads.

As a'result of my invention I provide a duplex tetrode arranged with a unitary cathode and focusing structure electrically grounded to a metal'envelope, a unitary screen grid electrically by-passed to the grounded cathode by means of a capacitance included in the vacuum chamber and functioning as the screen grid support, two separate and independent control grids with attached neutralizer elements, and anodes supported from the opposite end of the envelope from the other electrodes. When push-pull operation is employed, the two anode leads function with the anodes, as the elements of the anode resonant circuit formed by applying a shorting bar directly to these leads. All of the electrodes, except the anodes, are mounted on a header adjustable with respect to the other member of the vacuum retaining envelope on which the anodes are mounted. The final vacuum closure is by means of a compression gasket.

As a result of my invention I obtain a number of advances and advantages both circuitwise and electronically over conventional push-pull amplifiers. Among these advantages are:

(alLow impedance from screen grid to screen grid with attendant small radio frequency potential diiference;

(b) Low impedance between cathodes of the two tetrode sections obtained by means of a common cathode of small dimensions:

Low impedance between screen grid assembly and a grounded cathode obtained by means of reduced dimensions and a shuntin capacitance between screen grid and cathode included within the vacuum envelope;

Effective liquid cooling of all electrodes with small dimensions and compact structures; A better balanced push-pull amplifier because the two tetrode sections may be balanced with respect to each other with greater precision in manufacture than if two individual tetrodes were used; and finally Direct capacity neutralization from anodes to control grids for push-pull amplifier application by means of elements .of a very short length.

(g) Effective control of electron beams of large density with small control grid and screen rid currents.

Reduction of electron transit time at high frequencies by means of electrode configurations which permit the utilization of electron beams of large density together with small effective electrode spacings.

Increase in band width by means of electrode configurations which provide controlled electron beams of large den ity d permit large power dissipation per unit area at the collecting electrodes.

By means of my invention I have been able to provide an internally neutralized high frequency amplifier capable of a power output and at a frequency considerably in excess of conventional amplifier tubes. In one example of my invention, operating as a push-pull amplifier the device delivered a continuous output of 5000 watts at 300 megacycles with a band width in excess of 10 megacycles and a power gain of 10. This device can be operated at frequencies up to 600 megacycles. The average grid current is sufficiently small to permit successful operation as a grid modulated television amplifier at 300 megacycles. By means of the cathode and grid structures employed, cathode electron densities of 3.5 amperes per square centimeter are successfully controlled with control grid currents less than five percent of the anode current. Complete electrical stability and freedom from oscillation has been obtained when the tube is used as a push-pull amplifier.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device having an envelope containing a cathode means including a plurality of parallel elongated emitting elements lying in a plane for supplying a plurality of electron beams along parallel space paths, a control electrode next adjacent said emitting elements and having a plurality of flat elongated elements extending transversely of and between said paths and having the flat sides lying in a common plane close to said emitting elements and transversely to said electron paths, the elements of said control electrode lying parallel to said emitting elements. no part of said control electrode lying in the paths of said electrons, a screen electrode having a plurality of spaced elements lying parallel to and registering with said control electrode elements and lying between said beam paths, no part of said elements of said screen electrode lying in the path of said electrons and an electrode for receiving electrons from said cathode means, said cathode means and said other electrodes being closely spaced.

2. An electron discharge device having an envelope containing a cathode assembly for providing a plurality of parallel electron beams along space paths and comprising a planar focusing structure having a plurality of parallel slots in the surface thereof, and a cathode comprising a plurality of parallel elongated emitting elements lying in said slots but out of contact with the surfaces of said focusing structure defining said slots for providing a plurality of electron beams along said space paths, a control electrode next adjacent said emitting elements and having a plurality of flat elongated elements extending transversely of and between said space paths and having flat sides thereof lying in a common plane close to the surface of said focusing structure intermediate said slots, a screen electrode having a plurality of spaced elements lying parallel to and structure havinga plurality .of parallelz-slot in the surface thereof, and 'a cathode 'comprising a plurality of parallel elongated emitting elements lying in said slots but out of conta'ctwiththe surfaces of said focusing. structuredefining said'slots "for providing aplurality of telectron'beams along :said space paths, a control electrode having .a

plurality of flat elongated elements extending :transverselyof and between-said spa-cc pathsand having flatsides thereof "lying in 'a common plane close to the surface ofsaid focusing structure' intermediate said slots, a screen electrode having 1 a plurality of spaced elements lying paralleldo and registering with "said control electrode elements and lying between said space pathsran'dian electrode .for receiving electrons from .said cathode, said cathode and said wother electrodes being closely spaced, the surfaces of said planarifo'cusing structure between :said :slots having a concave transverse cross section.

4. An electron discharge devicehaving an envelope containing .a cathode assembly for proiding a plurality of parallel electronrbeams along space paths and comprising 'a, :pl'anar'focusing structure having 'a plurality of :parallel :slots in the :surface thereof, 1 and a cathode comprising: a plurality of parallel elongated flat remitting elements .lyinglin said slotslbut out of-conta'ct with the surfaces of said focusing structure defining said slots for providing 'a plurality "30f electron beams along said space paths, a controlelectrode havin a plurality.dfflatelongated elements "extending transversely of .and between said space paths and having flat sides :thereof dying ina common. plane closeito the surface of said focusing structure intermediate said slots,-:a :screen electrode having a plurality'ofspaced elements lying parallel :to and :registering with said -'con trol electrode elements, the elements Of :said screenelectrode having round transverse sections andllying:betweensaid space pathsan'd'an electrode for receivingelectrons fIfOIIlFSfiidcCfithOdB, said cathode and said other electrodes being closely spaced,'the surfaces'of'said planarfocusing structure between said slots having aconcave transverse section.

5. A cathode assemblyifor providing asplurality of oppositely directed electronbeams along space paths and comprising a planar focusing structure having on opposite sides thereof parallel slots in the surfaces thereof, a U-shaped cathode cathode structure received within said-slots but out of contact with the surfacesofsaid/focusing structure defining said slots, the :legs of :said U--shaped cathode structure being-received. in oppositely disposed slots.

6. A cathode assembly-forproviding agplur ality of oppositely directed electron beams and including an electron focusing structureincluding a-pair of registering plate-like elementsinsulated from each other and having on'the outer'faces thereof a plurality of longitudinally extending parallel slots, a- U- haped cathode filament assembly comrising a plurality of parallel Ushapedfilament like elements positioned within said; slots :but out of contact with the surfaces definingsaidslots, 75

'14 the :legs zofieach U=shaped filament-like element being-receivedlwith oppositely disposed slots.

7. A'cathodeassembly for providing a plurality 'of' oppositely directed electron beams along parallel spacapaths and comprising a planar focusing structure havingion opposite sides thereofparallel .slots'in the surfaces thereof, a U-shaped cathode structure comprisinga plurality 0f1Ushaped elements lying in parallelplanes and received within :saidslotsbut out of contact with the surfaces of said focusing structure defining said slots, and means for securing the ends'of the legs of said 'cathode'structure to opposite sides and adjacent onecdge ofsaidfocusing structure.

at. 'n cathode assembly for'providing a plurality of "oppositely directed electron beams and including an electron focusing structure having apair of registering 'plate like elements insulated from each other-and havingonthe outer faces thereof a plurality of longitudinally extending parallel slots,ja' U-shaped cathode assembly comprising a plurality of parallel U-shaped fiat filament-like elements within said slots,ithe adja'cent'free ends of each leg :of the 'U-shaped cathode lements beingsecuredtogether, the ends of opposite legs being secured to opposite focusingplate-like elements adjacent one edge thereof.

:19. A-cathode assembly forproviding a plurality of ,oppositelydirected electron beams along'ispace pathsandcomprising a..planar'focusing structure having on opposite sides thereof parallel slots inithe sufface'thereof, a u shaped cathode structurereceivedwithin said slots'but out of contact with the ssu'rfaces'of isaid focusing structure defining said slots, the opposite sidcs'of said focusingstructure being insulatedfrom each other, the ends-of the "legs :of said U-shaped cathode structure :being secured to opposite sides of said focusing, structure.

:10. :A cathode assembly for providing a plurality ofparallel electron beams along space paths .and comprising a, planar focusing structure having .a plurality of parallel slots in the surface thereof, and a cathode structure comprising a pluralitycf flat spaced parallelstraightfilaments received withinsaidslots but-out of contact with the surfaces of said planar focusing structure defining said slots, saidflat filaments having the :fiat surfaces lying in a :plane extending iparallel .to;the1-plane of :focusing structure and positioned closely adjacent the surface of said focusing structure.

:11. A cathodezassem'bly forproviding oppositely directed electron beams and having .an'electron :focusing structure including apair of registering plate-like elements insulated from each other 'andhavingonthe outer faces thereof longitudinally-extending parallel-slots, a .U shaped cathode having its legs within said slots, the free ends of ithedegsao'f *the'U-shaped cathode being secured to opposite plate-like elements adjacent one edge thereoflzapair of spaced oppositely disposed cool- .ingand supportingblocks-having cooling passagewaysiextending therethrough and providing between said blocks a 'U-shaped recess along one side thereof, said focusing structure'being partially received within said U--shaped slot and secured to saidcoo-ling block.

I2..Acathode assembly for providing a plurality of oppositely directed electron-beams and having an electron focusing structure including va' pair of plate-like elements insulated from each other "and having on the outer'faces thereof a plurality of longitudinally extending .parallel lslots, :a vU eshaped cathode assembly. comprising a plurality of parallel U-shaped filament-like elements within said slots, the free ends of the legs being secured to oppositely disposed plate-like elements and adjacent one edge thereof, and a pair of shield members extending from the secured ends of said cathode filaments and toward the closed end of said cathode filaments for shielding a portion of said cathode filaments.

13. A cathode assembly for providing a plur-ality of oppositely directed electron beams and including an electron focusing structure having a pair of registering plate-like elements insulated from each other and having on the outer faces thereof a plurality of longitudinally extending parallel slots, a U-shaped cathode assembly comprising a plurality of parallel U-shaped flat filament-like elements, the legs of which lie within said slots, the free ends of the legs being secured to opposite plate-like elements adjacent one edge thereof, and a pair of oppositely disposed cooling and supporting'blocks having cooling passageways extending therethrough and supporting said focusing structure and said cathode, and an envelope for said cathode and focusing structur" and including a metallic header member, said cooling block being secured to said header member.

14. A cathode assembly for providing oppositely directed electron beams and including an electron focusing structure including a pair of platelike elements insulated from each other and having on the outer faces thereof parallel slots, :a U-shaped cathode having its legs within said slots but out of contact with the surface of said focusing structure defining said slots, the free ends of the legs of the U-shaped cathode being secured to opposite plate-like elements adjacent one edge thereof, a pair of oppositel disposed cooling and supporting blocks having cooling passageways ex tending therethrough and supporting said focusing structure and U-shaped cathode, and an envelope for said cathode and focusing structure and including a metallic header member, said cooling blocks being secured to said header member, and tubular means extending through said header member and communicating with said cooling blocks for circulating a cooling medium through said passageways.

15. A control grid electrode comprising a hollow tubular member closed at one end and a plurality of spaced conductors extending transversely of and each separately secured at one end to said tubular member and lying parallel to each other and in the same plane, and a second tubular member of smaller transverse section than said first tubular member extending within said first tubular member for providing a cooling medium for said hollow tubular member and said conductors.

16. A control grid electrode comprising a hollow tubular member closed at one end and a plurality of spaced flat conductors each separately secured to said tubular member at one end and lying parallel to each other and in the same plane, and a second tubular member of smaller transverse section than said first tubular member extending within said first tubular member for providing a cooling medium for said hollow tubular member, said hollow tubular member having a stud extending therefrom in a plane transverse to the longitudinal axis of said hollow tubular member, and a fiat conducting member secured to the free end of said stud for providing a neutralizing condenser.

17. A unitary electrode structure comprising a pair of oppositely disposed U-shaped members lying in parallel planes, a plurality of parallel spaced conducting rod-like elements supported on the legs of each of said U-shaped members, and lying in a plane parallel to the plane of the U-shaped member, and end members extending between said oppositely disposed U-shaped members for maintaining said U-shaped members in rigid spaced relationship.

18. A unitary electrode structure comprising a pair of oppositely disposed U-shaped members lying in parallel planes, a plurality of spaced conducting rod-like elements extending parallel to each other from each of the legs of each of said U-shaped members, the rod-like elements supported by each U-shaped member lying in a plane parallel to the plane of the U -shaped member, the rod-like elements On each leg of :a U-shaped member extending toward but out of contact with the rod-like elements on the other leg, and end members extending between said oppositely disposed U-shaped members for maintaining said U-shaped members in rigid spaced relationship.

'19. An electrode structure U-shaped member, a plurality of spaced conducting rod-like elements extending parallel to each other from each of the legs of said U-shaped member, said rod-like elements lying in a plane parallel to the plane of the U-shaped member, the rod-like element on each leg extending toward but out of contact with a registering rod-like element on the other leg.

20. An electrode structure comprising a U-shaped member of substantial thickness and having comparatively wide legs, the inneredges of each being provided with offset portions extending from one side of said U-shaped member,

. a plurality of spaced parallel conducting rod-like elements extending from each of the ofiset portions and inwardly 0f the legs of the U-shaped member, said rod-like elements lying in a plane parallel to the plane of the U-shaped member, said rods extending toward but out of contact with each other.

21. A box-like unitary electrode structure comprising a pair of oppositely disposed U-shaped members of substantial thickness and havin comparatively wide legs, the inner edges of which are provided with inwardly extending ofiset portions, a plurality of spaced parallel conducting rod-like elements extending from each of the ofiset portions of each U-shaped member, and inwardly of the legs of the U-shaped members, said rod-like elements of each U-shaped member lying in a plane parallel to the plane of the U-shaped member, and end members coextensive with the legs of the U-shaped members extending between said oppositely disposed U-shaped members for maintaining said U-shaped members in rigid spaced relationship.

22. A unitary electrode structure comprising a pair of oppositely disposed U-shaped members of substantial thickness and lying in parallel planes, a plurality of spaced parallel conducting rod-like elements supported by the legs of each of said U-shaped members, the rod-like elements supported by each U-shaped member lying, in a plane parallel to the plane of the U-shaped member, and end members extending between said oppositely disposed U -shaped members for maintaining said U-shaped members in rigid spaced relationship, said U-shaped members having pasageways therethrough for permitting circulation of a cooling medium.

comprising a .positely directed electron 23., A unitary electrode, structure comprising a pair of oppositely disposed U-shaped members of substantial thickness and lying in parallel planes, a plurality of spaced parallel conducting rod-like elements supported by the, legs of each of said U-shaped members, the rod-lilac elements supported by each U -shaped member lying in a, plane parallel to the plane of the U-shaped member, and end members extending between said oppositely disposed U-shaped members for maintaining said U-shaped members in rigid spaced relationship, said U-shapedmembers having passageways therethrough for permitting circulation of a cooling medium, and tubular conducting means for said cooling medium communicating with said passageways.

24, In an electron discharge device, a cathode and screen grid electrode assembly including cathode assembly for providing a plurality of opbeams along parallel space paths and comprising a planar focusing structure having on opposite sides thereof parallel slots in the surfaces thereof, a U -shaped cathode structure, comprising a plurality of U-shaped elements lying in parallel planes received within said slots but'out of contact with the surfaces of said focusing structure defining said slots, and a box-like screen grid electrode surrounding said cathode and foe using structure and having electron permeable sides registering with the legs of said cathode, saidbox-like screen grid electrode being insulatingly secured to said cathode assembly.

25. In an electron discharge device, a cathode and screen grid electrode assembl including cathode assembly for providing a plurality of oppositely directed electron beams along space paths and including an electron focusing structure including a pair of registering plate-like elements insulated from each other and having on the outer faces thereof a plurality of longitudinally extending parallel slots, a U-shaped cathode filament assembly comprising a plurality of parallel U-shaped filament-like elements within said slots, and a screen electrode surrounding said cathode-and focusing electrode and comprising a unitary box-like structure having open sides, rod-like elements supported on said boxlike structure and extending across said open sides and registering with the space between said space paths, and being insulatingly secured to said cathod assembly.

26. ,An .anode electrode for an electron discharge device comprising a hollow member having a single continuous multi-channel passage extending therethrough providing a back and forth passage, a tubular member connected to and supporting said anode, one end of said. multi-channel passageway communicating with said tubular member and another tubular member within said first tubular member and communicating with the other end of said multi-ohannel passageway.

27. An anode electrode for an electron discharge device comprising a hollow member having a plurality of parallel ribs within said member, alternate ribs being offset longitudinally with respect to each other to form a single continuous multi-channel pass-age extending therethrough, a tubular member connected to and supporting said anode, one end of said multi-channel passageway communicating with said tubular member, and tubular means within said first tubular member and communicating with the other end of said multi-channel passageway, said inner tubular means comprising a pair of members telescoped over one another.

28. An anode electrode for an electron discharge device comprising a flat plate-like conducting element having one surface for receiving electrons and having on the opposit surface thereof a plurality of parallel ribs, alternate ribs being offset longitudinally with respect to each other, and a cooperating member of U-shape for receiving said ribs, the inside surface of said U-shaped member and said ribs providing atortuous continuous channel for the passage of a cooling medium, said U-shaped member having a chamber and passageways extending from said chamber to opposite sides of said tortuous channel for circulating a cooling medium therethrough.

29. An anode electrode for an electron discharge device comprising a hollow box-like member, a plurality'of parallel ribs within said boxlike member, alternate ribs being offset longitudinally with respect to each other for providing passageways between the ends of said ribs and the inside walls of said box-like member, whereby a continuous multi-channel passageway is provided through said box-like member, the walls of said box-like member having passageways extending therethrough and communicating with opposite ends of said multi-channel passageway.

30. An anode electrode for an electron discharge device comprising a hollow box-like member, a plurality of parallel ribs within said boxlike member, alternate ribs being offset longitudinally with respect to each other for providing passageways between the ends of said ribs and the inside walls of said box-like member, whereby a continuous multi-channel passageway is provided through said box-like member, said box-like member having an offset portion provided with a chamber and passageways extending from said chamber to opposite ends of said multi-channel passageway.

31. An electron discharge device having an envelope including a conducting header member, a cathode assembly and a screen electrode insulated from said cathode assembly, said cathode assembly and screen electrode being supported from said header member, said header member having a, plurality of apertures therethrough, and a plurality of leads extending from said cathode assembly through said header member, and a lead extending from said screen electrode and through an aperture and insulatingly sealed therein, and a control electrode positioned between said cathode assembly and screen electrode and. having a lead insulatingly supporting said control electrode from said header member and extending through another of said apertures and sealed therein, and a closure member for said header member providing an envelope, an anode, a lead extending through said closure member and supporting said anode adjacent said screen electrode, said cathode assembly, Said control and screen electrodes and said anode all having passageways extending therethrough through which a cooling medium may be circulated,said leads comprising tubular members into which and out of which a cooling medium may be circulated into and out of said cathode assembly, control and screen electrodes and said anode.

32. An electrode assembly for providing a plurality of oppositely directed electron beams and including an electron focusing structure having a pair of registering plate-like elements insulated from each other and having on the outer faces thereof a plurality of longitudinally extending parallel slots, a U-shaped cathode assembly comlike elements, the legs of which lie within said prising a plurality of parallel U-shaped filamentsides of said screen electrode.

33. An electron discharge device having an envelope closed by a metal header, a fiat cathode within said envelope, a control grid electrode positioned at each side of said cathode, each grid electrode comprising a hollow tubular member closed at one end and a plurality of spaced flat conductors secured to said tubular member near to the end of said L-shaped lug for providing a. neutralizing condenser, said header member having an aperture extending therethrough, the

cathode, the plate on each control grid electrode extending toward but out of contact with the anode on the other side of the cathode.

dium for said hollow tubular member, said header member havin an aperture extending therethrough, the hollow tubular members of said grids extending through and insulatingly sealed in said ing a plurality of parallel slots in'the surface thereof, and a cathode comprising a plurality of 36. An electron discharge device having an envelope containing a cathode assembly for providing a plurality of electron beams along space 37. An electron discharge device havin an envelope containing a cathode assembly for providing a plurality of parallel electron beams along space paths and comprising a focusing structure having a plurality of parallel slots in the surface thereof, and a cathode comprising a plurality of elongated emitting elements lying in said slots ing structure defining said slots for providing a plurality of electron beams along said space paths, a control electrode next adjacent said emitting elements and having a plurality of elongated elesaid focusing structure intermediate said slots and an electrode for receiving electrons from said cathode, said cathode and said other electrodes being closely spaced.

HOWARD R. HEGBAR. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

